This invention relates to production tubing strings used in oil wells that are being produced by rod pumping, which is the conventional technique for pumping oil from underground reservoirs. At the surface, a motor drives a walking beam which is connected to a polished rod that is in turn connected to a string of sucker rods which extend down the borehole to support the downhole pump. As the motor runs, the walking beam raises and lowers the polished rod and string of sucker rods which causes the pump to lift the fluid from the reservoir up to the surface.
Historically, wells which are produced with conventional rod pumping units have evidenced problems with tubing and/or rod or rod coupling failures due to the abrasion of the rods and rod couplings on the tubing walls as the rod string reciprocates. These failures may be accelerated by the presence of corrosive elements and/or by the deviation of the well bore in drilling or through subsidence. The present invention greatly reduces these failures.
In accordance with the present invention the production tubing joints in a rod-pumped well are lined with polymer liners which reduce the abrasion and failure of the tubing joints caused by the reciprocating rods. The polymer liners, such as high density polyethylene liners, have a coefficient of friction which is far superior to the coefficient of friction of steel tubing. Further, when the polyethylene liner is wetted by the produced fluid, susceptibility to abrasion is further reduced.
Although the lining of pipe and tubing with polymer liners for corrosion control has been practiced heretofore, the lining of tubing strings in rod-pumped wells to reduce the abrasion and failure of the tubing joints caused by the reciprocating rods is novel. For example, liners have been installed in pipelines for the transportation of oil, water, gas and sewage for some time. In the application of polymer lined tubing for oil field tubing strings, the application has been for the protection of tubing utilized for injection strings, water disposal strings, or production strings which flow or which are produced with electric submersible pumps.
The present invention achieves the substantial benefits of protecting the tubing string on a rod pumped well from the detrimental effects to and failures of the production tubing caused by the reciprocating rods as well as protecting the tubing against corrosive elements such as salt water, hydrogen sulfide, carbon dioxide and other corrosive elements produced in oil wells.
It is thus an objective of this invention to utilize polymer liners in the tubing production strings of rod pumping wells for the purpose of eliminating metal to metal contact between the rods, rod couplings and the production tubing string, thereby reducing the frequency of failures due to rod wear, rod coupling wear, and/or production tubing string wear.
Still another object of this invention is to provide protection of the production tubing string of an oil well produced by rod pumping from the corrosive elements of the components of the produced fluid and thereby provide an opportunity to reduce the production costs by reducing the chemical treatment of the well's producing string.